Drive shaft for compressor

ABSTRACT

A compressor assembly including a motor having a stator and a rotor, and a drive shaft having an elongate central portion and first and second end portions located on opposite ends of the central portion. The shaft defines a rotational axis and extends through the rotor with the central portion rotationally secured to the rotor and the first and second end portions disposed proximate opposite ends of the motor. First and second compressor mechanisms are disposed proximate opposite ends of the motor and are operatively coupled to the first and second end portions, respectively, of the shaft. First end portion, second end portion and central portion define respective first, second and third cross-sectional configurations oriented perpendicular to the rotational axis. Each of first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of the third cross-sectional configuration relative to the rotational axis.

PRIORITY REFERENCE

This application claims the benefit of priority under 35 U.S.C. §119(e) to provisional application Ser. No. 60/589,051, filed in the name of Zer Kai Yap on Jul. 19, 2004.

BACKGROUND

The present invention relates generally to hermetic compressor assemblies having two compressor mechanisms driven by a single motor and, more particularly, to hermetic compressor assemblies having an improved drive shaft operably coupling the motor to the two compressor mechanisms.

Compressor assemblies having two compressor mechanisms operably coupled to a single motor by a drive shaft are known. In many such assemblies, the drive shaft includes two integral eccentric portions defined at one end of the shaft. These eccentric portions are often machined into, or integrally molded with, the shaft such that they are unitary with the shaft. The motor includes a rotating rotor which defines a central bore extending through the rotor along a rotational axis. The end of the drive shaft opposite the eccentric portions extends into the bore and is affixed to the rotor for rotation therewith. Each of the integral eccentric portions operably engages one of the two compressor mechanisms, thereby mounting both of the two compressor mechanisms at one end of the drive shaft and adjacent one end of the motor.

Still other dual mechanism compressor assemblies are known in which the unitary eccentric portions are defined at opposite ends of the drive shaft. In such assemblies, the two compressor mechanisms are operably mounted about the eccentric portions at opposite ends of the shaft and are thereby positioned adjacent opposite ends of the motor. Such an arrangement may be used to improve the balance of the compressor assembly, which may reduce the vibration and lower noise. However, oftentimes the eccentric portions define a larger cross-section than that of the drive shaft. These eccentric portions cannot fit through the bore of the rotor and, consequently, it is difficult to assemble such a compressor using a one-piece shaft. Instead, these compressor mechanisms require a two-piece drive shaft that is joined inside the rotor. The two-piece drive shaft design may be less rigid than the one-piece design, thereby causing the shaft to bend or deflect. Deflection of the shaft may cause the misalignment of the bearings, which ultimately may result in leaks and housing deformation.

Due to the problems associated with a drive shaft having unitary eccentric portions, a need remains for a hermetic compressor assembly having two compressor mechanisms operably engaged to opposite ends of a drive shaft without the use of eccentric portions unitarily defined in the drive shaft.

SUMMARY OF THE INVENTION

The present invention provides a compressor assembly that uses a shaft, which does not include unitarily defined eccentric portions at both ends and which extends through the motor to operably engage a compression mechanism at each end of the shaft on the opposite ends of the motor.

The compressor assembly comprises, in one form thereof, a motor including a stator and a rotor, and a drive shaft including an elongate central portion and first and second end portions located on opposite ends of the central portion. The drive shaft defines a rotational axis. First end portion, second end portion and central portions define respective first, second and third cross-sectional configurations oriented perpendicular to the rotational axis. Each of the first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of the third cross-sectional configuration relative to the rotational axis. The drive shaft extends through the rotor with the central portion being rotationally secured to the rotor, the first end portion disposed proximate a first end of the motor and the second portion disposed proximate a second end of the motor. A first compressor mechanism is disposed proximate the first end of the motor and is operatively coupled to the first end portion of the drive shaft wherein the first end portion rotationally drives the first compressor mechanism. A second compressor mechanism is disposed proximate the second end of the motor and is operatively coupled to the second end portion of the drive shaft wherein the second end portion rotationally drives the second compressor mechanism.

In another form, the compressor assembly comprises a motor including a stator and a rotor, and a drive shaft comprising an elongate central portion and first and second end portions located on opposite ends of the central portion. The drive shaft defines a rotational axis. The first end portion, second end portion and central portion define first, second and third cross-sectional configurations, respectively, oriented perpendicular to the rotational axis. Each of the first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of the third cross-sectional configuration relative to the rotational axis. The first and second end portions each define a substantially similar non-circular cross-sectional configuration. The first and second configurations are rotationally offset by 180 degrees relative to the rotational axis. The drive shaft extends through the rotor with the central portion being rotationally secured to the rotor, the first end portion disposed proximate a first end of the motor and the second end portion disposed proximate a second end of the motor. A first rotary compressor mechanism is disposed proximate the first end of the motor and operatively coupled to the first end portion of the drive shaft wherein the first end portion rotationally drives the first compressor mechanism. A second rotary compressor mechanism is disposed proximate the second end of the motor and is operatively coupled to the second end portion of the drive shaft wherein the second end portion rotationally drives the second compressor mechanism.

The present invention also provides a method of assembling a compressor assembly. The method, in one form thereof, includes providing a motor having a stator and a rotor, the rotor having an axially extending central bore, forming a drive shaft with an integral elongate member wherein the drive shaft includes an elongate central portion and first and second end portions located on opposite ends of the central portion, the drive shaft defining a rotational axis, the first end portion defining a first cross-sectional configuration oriented perpendicular to the rotational axis, the second end portion defining a second cross-sectional configuration oriented perpendicular to the rotational axis and the central portion defining a third cross-sectional configuration oriented perpendicular to the rotational axis wherein each of the first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of the third cross-sectional configuration relative to the rotational axis, securing the drive shaft to the rotor by thermally expanding the rotor, inserting one of the first and second end portions of the drive shaft through the central bore of the rotor wherein the first end portion of the drive shaft accessible from a first end of the rotor and the second end portion of the drive shaft is accessible from a second end of the rotor, and allowing the rotor to cool and rotationally secure the drive shaft in the central bore of the rotor in a shrink-fit engagement, operably coupling a first compressor mechanism to the first end portion of the drive shaft wherein the drive shaft rotationally drives the first compressor mechanism, and operably coupling a second compressor mechanism to the second end portion of the drive shaft wherein the drive shaft rotationally drives the second compressor mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a sectional view of a dual mechanism hermetic compressor assembly according to the present invention;

FIG. 2 is a top sectional view of the compressor assembly of FIG. 1 taken along lines 2-2;

FIG. 3 is an inner end perspective view of the crankcase/shaft assembly of the compressor assembly of FIG. 1;

FIG. 4 is an outside end view of the compressor mechanism of the compressor assembly of FIG. 1;

FIG. 5 is a perspective view of the shaft roller assembly of the compressor assembly of FIG. 1;

FIG. 6 is a perspective view of the inner roller of the compressor assembly of FIG. 1;

FIG. 7 is a perspective view of the shaft of the compressor assembly of FIG. 1;.

FIG. 8 is a perspective view of a shaft according to another embodiment of the present invention;

FIG. 9 is a perspective view of a shaft/eccentric/piston assembly according to the embodiment of FIG. 8; and

FIG. 10 is a sectional view of compressor assembly with the assembly in FIG. 9.

Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplification set out herein illustrates embodiments of the invention, in several forms, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise forms disclosed.

DESCRIPTION OF THE PRESENT INVENTION

Referring first to FIG. 1, compressor assembly 10 generally includes first compressor mechanism 14, second compressor mechanism 16 and motor assembly 18, all of which are disposed within interior volume 13 of housing 12. Housing 12 includes first and second end members 12 a, 12 b and cylindrical main member 12 c. Housing members 12 a, 12 b, 12 c are hermetically sealed to one another to define interior volume 13.

Still referring to FIG. 1, motor assembly 18 defines first end 26 and opposite second end 28 and includes rotor 20, stator 22 and stator windings 24. Motor assembly 18 is connected to a power source (not shown) which drives the rotation of rotor 20 about rotational axis A-A. Elongate drive shaft 30 extends through motor assembly 18 and operably connects first and second compressor mechanisms 14, 16 to motor assembly 18. Drive shaft 30 extends through a central bore in rotor 20 along rotational axis A-A and is rotatably secured to rotor 20 for rotation therewith about axis A-A. Shaft 30 may be secured to rotor 20 using conventional shrink-fit methods. One such method includes thermally expanding rotor 20, inserting shaft 30 through the central bore of thermally expanded rotor 20, and allowing rotor 20 to cool and, thus, shrink around shaft 30 to secure shaft 30 within rotor 20.

As illustrated in FIG. 1, drive shaft 30 is integrally formed as a single unit and defines first end portion 32, elongate central portion 34 and second end portion 36. First and second end portions 32, 36 of shaft 30 protrude from respective first and second ends 26, 28 of motor assembly 18 and operably engage first and second compressor mechanisms 14, 16, respectively, thereby positioning first and second compressor mechanisms 14, 16 proximate opposite ends of motor assembly 18. The positioning of first and second compressor mechanisms 14, 16 proximate opposite ends of motor assembly 18 provides improved balance in comparison to an assembly wherein one or more compressors are positioned proximate a single end of the motor. This improved balance may result in lower vibration and, ultimately, lower noise. The configuration of first and second end portions 34, 36 and their engagement with first and second compressor mechanisms 14, 16 is described in further detail below.

Turning to FIGS. 1 and 2, first and second compressor mechanisms 14, 16 are identical rotary-type mechanisms and each generally includes crankcase 38, annular cylinder block 40, top member 42, and roller assembly 43. Cylinder block 40 is mounted between crankcase 38 and top member 42. Top member 42, cylinder block 40 and crankcase 38 are secured to one another by fasteners (not shown) which extend through fastener-receiving holes 42 a, 40 a, 38 a of top member 42, cylinder block 40, and crankcase 38, respectively. Cylinder block 40 defines an inside wall which cooperates with crankcase 38 and top member 42 to form compression chamber 52 in which a compressible fluid, such as a refrigerant, may be compressed.

As shown in FIGS. 1 and 2, roller assembly 43 is disposed within compression chamber 52 and includes eccentric inner roller 44 and main roller 48 rotatably mounted about eccentric inner roller 44. Inner roller 44 is operably coupled to drive shaft 30, the rotation of which causes roller assembly 43 to orbit within compression chamber 52. The engagement between drive shaft 30 and inner roller 44 is described in further detail below. Needle roller bearings (not shown) may be mounted between inner roller 44 and main roller 48 to facilitate the rotation of main roller 48 about inner roller 44. Main roller 48 defines a cylindrical outer surface which travels along and sealingly engages the inside wall of cylinder block 40 to give compression chamber 52 an evolving crescent shape. Sliding vane 50 reciprocates within slot 51 defined in cylinder block 40 and engages main roller 48.

Referring to FIG. 1, crankcase 38 of each of first and second mechanisms 14, 16 is mounted on respective first and second ends 26, 28 of motor assembly 18, thereby securing first and second compressor mechanisms 14, 16 to opposite ends of motor assembly 18. Crankcase 38 may be mounted to motor assembly 18 in any conventional manner. One such manner involves inserting bolts (not shown) through holes 39 (FIGS. 2-4), which extend through legs 41 of crankcase 38, and engaging the bolts to threaded holes (not shown) in stator 22.

As illustrated in FIGS. 1 and 3-4, crankcase 38 defines a substantially cylindrical perimetrical sidewall 45 that firmly and sealingly bears against main housing member 12 c. The firm engagement between the sidewall of crankcase 38 and main housing member may be achieved by conventional shrink-fit methods. As a result of the sealed engagement between crankcase 38 and housing 12, the crankcases 38 of first and second compression mechanisms 14, 16 cooperate with one another to sealingly divide interior plenum 13 into first discharge plenum 66, second discharge plenum 68 and suction plenum 69. First discharge plenum 66 includes that portion of interior plenum 13 located between crankcase 38 of first compression mechanism 14 and first end member 12 a of housing 12. Second discharge plenum 68 includes the portion of interior plenum 13 located between crankcase 38 of second compression mechanism 16 and second end member 12 b of housing 12. Suction plenum 69 comprises the portion of interior plenum 13 located between the crankcases of first and second compression mechanisms 14, 16. Suction inlet 15 extends through main housing member 12 c and communicates with suction plenum 69. First and second discharge tubes 70, 72 extend through first and second end housing members 12 a, 12 c, respectively, and communicate with respective discharge plenums 66, 68.

Referring now to FIGS. 1 and 4, top member 42 of each of first and second compression mechanisms 14, 16 includes discharge port 56, which provides fluid communication between compression chambers 52 of first and second compression mechanisms 14, 16 and respective discharge plenums 66, 68. As illustrated in FIG. 4, the outer surface of top member 42 defines recess 58 which surrounds and extends from discharge port 56. Discharge valve assembly 60 fits within recess 58 and includes flexible discharge valve member 62, rigid valve retainer 64, and valve fastener 65. Valve assembly 60 is mounted within recess 58 by valve fastener 65, which engages valve fastener opening 67.

Referring to FIGS. 1 and 3, crankcase 38 of each of first and second compression mechanisms 14, 16 defines inlet opening 74 by which the refrigerant flows into compression chamber 52. Compressor assembly 10 can be configured as either a single-stage compressor, in which the refrigerant enters both first and second compressor mechanisms 14, 16 at suction pressure and is compressed therein and discharged at a final pressure, or a two-stage compressor, in which the refrigerant enters first compressor mechanism 14 at suction pressure, is compressed to an intermediate pressure, and is discharged to second compressor mechanism 16 wherein the refrigerant is further compressed to and discharged at a final pressure. In first compressor mechanism 14, inlet opening 74 communicates the refrigerant from suction plenum 69 to compression chamber 52. In second compressor mechanism 16, inlet opening 74 is in fluid communication with compression chamber 52 and either suction plenum 69, if compressor assembly 10 is a single-stage compressor, or first discharge tube 70, if compressor assembly is a two-stage compressor. If compressor assembly is a two-stage compressor, first discharge tube 70 may extend from first end housing member 12 a, through main housing member 12 c, and join inlet opening 74 of second compressor mechanism 16.

Referring now to FIGS. 5-7, the configuration of drive shaft 30 and its engagement with first and second compressor mechanisms 14, 16 will now be described. As noted above, drive shaft 30 is a unitary elongate member including elongate central portion 34 and first and second end portions 32, 36 located on opposite ends of central portion 34. Drive shaft 30 may be made of steel or any other rigid material sufficient to withstand the pressures and forces generated during operation without deformation or deflection. Drive shaft 30 extends along and rotates about rotational axis A-A. Each of first end portion 32, central portion 34 and second end portion 36 defines a cross-sectional configuration oriented perpendicular to rotational axis A-A. As shown in FIGS. 5 and 7, the cross-sectional configuration of central portion 34 is substantially circular, while the cross-sectional configurations of first and second end portions 32, 36 are substantially non-circular. The cross-sectional configurations of first and second end portions 32, 36 define a pair of opposing planar flats 33 which give the cross-sectional configurations of first and second end portions 32, 36 an outer perimeter that is disposed radially within the outer perimeter of the cross-sectional configuration of central portion 34 relative to the rotational axis A-A. The cross-sectional configuration of first and second end portions 32, 36 may be machined into shaft 30 or, alternatively, shaft 30 may be molded to form by any conventional method, such as by investment casting.

Turning to FIG. 6, inner roller 44 of each of the roller assemblies 43 of the first and second compressor mechanisms 14, 16 includes an outer cylindrical surface which defines roller axis A₁-A₁. A shaft mounting opening 46 extends through inner roller 44 along a line parallel to but spaced apart from the corresponding roller axis. Opening 46 has a substantially non-circular configuration, which includes a pair of opposing flats 47. The overall configuration of opening 46 is complementary to the cross-sectional configurations of first and second end portions 32, 36 of shaft 30, such that first and second end portions 32, 36 of shaft 30 may be slip-fit into opening 46 of roller 44 of first and second compressor mechanisms 14, 16, respectively. This slip-fit engagement prevents relative rotation of shaft 30 with respect to inner roller 44. Because opening 46 is offset from the corresponding roller axis, the rotation of shaft 30 imparts an orbiting motion to inner roller 44.

As shown in FIG. 1, first and second end portions 32, 36 of drive shaft 30 extend through and are journaled in crankcase 38 of first and second compression mechanisms 14, 16, respectively. Roller 44 of first and second compressor mechanisms 14, 16 is mounted, as described above, on first and second end portions 32, 36 of shaft 30. As shown in FIG. 5, roller 44 of first and second compressor mechanisms 14, 16 may be oriented on shaft 30 such that roller axis A₁-A₁ of each of first and second compressor mechanisms 14, 16 are positioned diametrically opposite one another relative to rotational axis A-A. Such an orientation may aid in rotationally balancing shaft 30. In addition or in the alternative, the cross-sectional configurations of first and second end portions 32, 36 may be oriented so as to be rotationally offset from one another relative to rotational axis A-A. More specifically, the cross-sectional configurations of each of first and second end portions 32, 36 defines a line of symmetry which divides the cross-sectional configuration into two symmetrical halves. As shown in FIG. 7, the cross-sectional configurations of first and second end portions 32, 36 may be oriented such that the line of symmetry of first end portion 32 is rotationally offset from the line of symmetry of second end portion 36 by 180° relative to rotational axis A-A.

In alternative embodiments, the cross-sectional configurations of first and second end portions and their corresponding shaft receiving openings may take different shapes. For instance, first and second end portions and their corresponding shaft receiving openings may be square, semi-circular, or pentagonal in cross-section.

As illustrated in FIGS. 1 and 2 and described above, both first and second compressor mechanisms 14, 16 may be rotary-type compression mechanisms. Alternatively, first and second compressor mechanisms may be any type of compression mechanism, including reciprocating-piston mechanisms, orbiting-scroll mechanisms, and rotary-screw mechanisms. For instance, first and/or second compressor mechanisms could be an orbiting-scroll mechanism such as that disclosed in U.S. Pat. No. 5,013,225 to Richardson, Jr. which is assigned to Tecumseh Products Company, the assignee of the present invention and which is hereby incorporated by reference. In this case, the shaft receiving opening may be defined in the hub of the orbiting plate and the shaft may be slip-fit into the opening. It should also be understood that first and second compressor mechanisms need not necessarily be identical to one another. In other words, first compressor mechanism may be of a different type than that of second compressor mechanism.

In operation, rotor 20 rotates about rotational axis A-A which in turn causes the rotation of shaft 30 about axis A-A. The rotation of shaft 30 imparts a rotational force on roller 44 of both first and second compressor mechanisms 14, 16. This rotational force is translated into an orbiting motion of rollers 44 simultaneously within chambers 52 of both first and second compressor mechanisms 14, 16. As roller 44 orbits within chamber 52, it engages sliding vane 50 and the inside wall of cylinder block 40 to cause the crescent-shaped chamber 52 to expand and contract in size and, thereby, draw in and compress the refrigerant within the chambers 52 of first and second compressor mechanisms 14, 16. The refrigerant is drawn into suction plenum 69 at suction pressure via suction inlet 15.

Assuming compressor assembly 10 is a two-stage compressor, the refrigerant flows from suction plenum 69 to compression chamber 52 of first compressor mechanism 15 via inlet opening 74. The refrigerant is compressed within compression chamber 52 of first compressor mechanism 14. When the pressure of the refrigerant within chamber 52 of first compressor mechanism 14 reaches a pressure sufficient to bias valve member 62 away from port 56, the refrigerant is discharged through discharge port 56 into first discharge plenum 66. From discharge plenum 66 the refrigerant enters discharge tube 70 and flows to second compressor mechanism 16 where it enters compression chamber 52 of second compressor mechanism 16 through inlet opening 74 of second compressor mechanism 16. The refrigerant is then compressed to a higher pressure and is discharged through discharge port 56 of second compressor mechanism 16 when the pressure within compression chamber 52 of second compressor mechanism 16 is sufficient to bias valve member 62 away from port 56. From second discharge plenum 68 the refrigerant enters second discharge tube 72 and exits compressor assembly 10.

If compressor assembly 10 is configured as a single-stage compressor, the refrigerant flows from suction plenum 69 into the compression chambers 52 of both first and second compressor mechanisms 14, 16. The refrigerant is then compressed within compression chambers 52 of first and second compressor mechanisms 14, 16 and is discharged through discharge ports 56 and into first and second discharge plenums 66 and 68, respectively. From discharge plenums 66, 68 the refrigerant enters discharge tubes 70, 72, respectively, and exits the compressor assembly 10.

In an alternative embodiment shown in FIGS. 8-10, compressor 110 generally includes motor assembly, 18, first and second compressor mechanisms 114, 116 and shaft 130, which also does not include unitarily defined eccentric portions. As shown in FIG. 8, shaft 130 includes a one-piece elongate member defining first end portion 132 and opposite second end portion 136. Shaft 130 extends through a central bore in rotor 20 of motor assembly 18 along rotational axis A-A and is rotatably secured to rotor 20 for rotation therewith. First and second end portions 132, 136 of shaft 130 are positioned adjacent opposite ends of motor assembly 18. Each of first and second end portions 132, 136 define a central opening 138 extending axially into first and second end portions 132, 136 along rotational axis A-A. Groove 140 extends around the circumference of each of first and second end portions 132, 136 (not shown at end portion 132) and extends inward toward central opening 138.

First and second compressor mechanisms 114, 116 each include eccentric member 144. Eccentric member 144 of first and second compressor mechanisms 114, 116 each includes substantially cylindrical eccentric portion 144 a which defines member axis A₁-A₁, and a linking rod 144 b extending from eccentric portion 144 a along a rod axis parallel to but spaced apart from member axis A₁-A₁. Linking rod 144 b is sized and shaped to fit within central opening 138 and defines groove 146, which extends around the circumference of linking rod 144 b. Grooves 140 and 146 cooperate to define a lubrication passage. Opening 162 is formed in groove 146 and acts as a lubrication passage for delivering lubricant to grooves 140 and 146. Eccentric member defines a lubrication passage 160 extending through linking rod 144 b and eccentric portion 144 a along the rod axis.

An eccentric member 144 may be mounted to each of first and second end portions 132, 136 of shaft 130 by press fitting linking rod 144 b into central opening 138. Alternative means may be provided for securing rod 144 b in central opening 138. To achieve optimum balance eccentric members 144 may be oriented on shaft 130 such that member axis A₁-A₁ of each of first and second compressor mechanisms 114, 116 are positioned diametrically opposite one another relative to rotational axis A-A.

As illustrated in FIGS. 9-10, first and second compressor mechanisms 114, 116 may be reciprocating piston-type compressor mechanisms. First and second compressor mechanisms 114, 116 each includes piston 149 which operably engages eccentric member 144 through linkage key 150. Linkage key 150 includes a ring portion 150 a which is rotatably mounted about cylindrical eccentric portion 144 a of eccentric member 144. Ring portion 150 a includes a lubrication passage 164 for communicating lubrication fluid to the mating surfaces of ring portion 150 a and eccentric portion 144 a. Linkage key also includes a linkage arm 150 b which extends from linkage ring and engages piston 149 in a conventional manner. The rotation of shaft 130 about rotational axis A-A imparts a rotational force on eccentric member 144 causing eccentric member 144 to orbit about rotational axis A-A. The orbiting motion of eccentric member 144 imparts a reciprocating motion to piston 149 within cylindrical chamber 148 through linkage key 150.

While FIGS. 9-10 illustrate compressor mechanisms 114 and 116 as reciprocating piston-type mechanisms, it is contemplated that other compressor mechanisms may be used. For instance, member 144 could serve as the inner roller of a rotary-type compressor mechanism and, therefore, a rotary-type compressor mechanism could be mounted to the opposite ends of drive shaft 130.

While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. 

1. A compressor assembly comprising: a motor including a stator and a rotor; a drive shaft comprising an integral elongate member defining an elongate central portion and first and second end portions located on opposite ends of said central portion, said drive shaft defining a rotational axis, said first end portion defining a first cross-sectional configuration oriented perpendicular to said rotational axis, said second end portion defining a second cross-sectional configuration oriented perpendicular to said rotational axis and said central portion defining a third cross-sectional configuration oriented perpendicular to said rotational axis wherein each of said first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of said third cross-sectional configuration relative to said rotational axis, said drive shaft extending through said rotor with said central portion being rotationally secured to said rotor, said first end portion disposed proximate a first end of said motor and said second portion disposed proximate a second end of said motor; a first compressor mechanism disposed proximate said first end of said motor and operatively coupled to said first end portion of said drive shaft wherein said first end portion rotationally drives said first compressor mechanism; and a second compressor mechanism disposed proximate said second end of said motor and operatively coupled to said second end portion of said drive shaft wherein said second end portion rotationally drives said second compressor mechanism.
 2. The compressor assembly of claim 1 wherein said first and second compressor mechanisms are rotary compressor mechanisms.
 3. The compressor assembly of claim 2 wherein said first and second compressor mechanisms respectively include first and second rollers respectively mounted on said first and second end portions of said drive shaft wherein said first and second rollers each have an outer cylindrical surface respectively defining first and second roller axes wherein said first and second roller axes are oriented parallel to said rotational axis, each of said first and second roller axes being spaced from said rotational axis by a common distance and wherein said first roller axis is positioned diametrically opposite said second roller axis relative to said rotational axis.
 4. The compressor assembly of claim 1 wherein said first and second end portions each define a substantially similar non-circular cross-sectional configuration, said first and second configurations being rotationally offset by 180 degrees relative to said rotational axis.
 5. The compressor assembly of claim 2 wherein said first and second compressor mechanisms respectively include first and second rollers respectively mounted on said first and second end portions of said drive shaft wherein said first and second rollers each have an outer cylindrical surface respectively defining first and second roller axes wherein said first and second roller axes are oriented parallel to said rotational axis, each of said first and second roller axes being spaced from said rotational axis by a common distance.
 6. The compressor assembly of claim 5 wherein said central portion is substantially cylindrical and said first and second end portions each define a substantially similar non-circular cross-sectional configuration, said first and second configurations being rotationally offset by 180 degrees relative to said rotational axis.
 7. The compressor assembly of claim 6 wherein said central portion of said drive shaft is secured with said rotor in a shrink fit engagement.
 8. A compressor assembly comprising: a motor including a stator and a rotor; a drive shaft comprising an integral elongate member defining an elongate central portion and first and second end portions located on opposite ends of said central portion, said drive shaft defining a rotational axis, said first end portion defining a first cross-sectional configuration oriented perpendicular to said rotational axis, said second end portion defining a second cross-sectional configuration oriented perpendicular to said rotational axis and said central portion defining a third cross-sectional configuration oriented perpendicular to said rotational axis wherein each of said first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of said third cross-sectional configuration relative to said rotational axis and said first and second end portions each define a substantially similar non-circular cross-sectional configuration, said first and second configurations being rotationally offset by 180 degrees relative to said rotational axis, said drive shaft extending through said rotor with said central portion being rotationally secured to said rotor, said first end portion disposed proximate a first end of said motor and said second end portion disposed proximate a second end of said motor; a first rotary compressor mechanism disposed proximate said first end of said motor and operatively coupled to said first end portion of said drive shaft wherein said first end portion rotationally drives said first compressor mechanism; and a second rotary compressor mechanism disposed proximate said second end of said motor and operatively coupled to said second end portion of said drive shaft wherein said second end portion rotationally drives said second compressor mechanism.
 9. The compressor assembly of claim 8 wherein said first and second compressor mechanisms respectively include first and second rollers respectively mounted on said first and second end portions of said drive shaft wherein said first and second rollers each have an outer cylindrical surface respectively defining first and second roller axes wherein said first and second roller axes are oriented parallel to said rotational axis, each of said first and second roller axes being spaced from said rotational axis by a common distance and wherein said first roller axis is positioned diametrically opposite said second roller axis relative to said rotational axis.
 10. The compressor assembly of claim 8 wherein said drive shaft is substantially rotationally balanced.
 11. The compressor assembly of claim 10 wherein said central portion is substantially cylindrical and said first and second end portions each define a substantially similar non-circular cross-sectional configuration, said first and second configurations being rotationally offset by 180 degrees relative to said rotational axis.
 12. The compressor assembly of claim 11 wherein said central portion of said drive shaft is secured with said rotor in a shrink fit engagement.
 13. A method of assembly a compressor assembly, said method comprising: providing a motor having a stator and a rotor, the rotor having an axially extending central bore; forming a drive shaft with an integral elongate member wherein the drive shaft includes an elongate central portion and first and second end portions located on opposite ends of the central portion, said drive shaft defining a rotational axis, said first end portion defining a first cross-sectional configuration oriented perpendicular to said rotational axis, said second end portion defining a second cross-sectional configuration oriented perpendicular to said rotational axis and said central portion defining a third cross-sectional configuration oriented perpendicular to said rotational axis wherein each of said first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of said third cross-sectional configuration relative to said rotational axis; securing the drive shaft to the rotor by thermally expanding the rotor, inserting one of the first and second end portions of the drive shaft through the central bore of the rotor wherein the first end portion of the drive shaft accessible from a first end of the rotor and the second end portion of the drive shaft is accessible from a second end of the rotor, and allowing the rotor to cool and rotationally secure the drive shaft in the central bore of the rotor in a shrink-fit engagement; operably coupling a first compressor mechanism to the first end portion of the drive shaft wherein the drive shaft rotationally drives the first compressor mechanism; and operably coupling a second compressor mechanism to the second end portion of the drive shaft wherein the drive shaft rotationally drives the second compressor mechanism.
 14. The method of claim 13 wherein the first and second compressor mechanisms are rotary compressor mechanisms and wherein operably coupling the first and second compressor mechanisms to the first and second end portions of the drive shaft includes respectively mounting first and second rollers on the first and second end portions wherein each of the first and second rollers has an outer cylindrical surface respectively defining first and second roller axes, each of the first and second roller axes being spaced from the rotational axis by a common distance and wherein the first roller axis is positioned diametrically opposite the second roller axis relative to the rotational axis.
 15. The method of claim 13 wherein the first and second end portions each define a substantially similar non-circular cross-sectional configuration, the first and second configurations being rotationally offset by 180 degrees relative to said rotational axis.
 16. The method of claim 13 wherein the drive shaft is substantially rotationally balanced.
 17. The method of claim 16 wherein the central portion is substantially cylindrical and the first and second end portions each define a substantially similar non-circular cross-sectional configuration, the first and second configurations being rotationally offset by 180 degrees relative to the rotational axis. 